Using Notepad to Troubleshoot Files that Won’t Open

A common occurrence in technical support are user’s that receive files that are missing file extensions. Often times, you can open the file in Notepad (or any other text reader) and scan the top of data for printable strings, i.e. readable text, that allude to the application or file type it is. For example, an image file, portable network graphics:
A PDF:
Some details about the PDF:
Sometimes, you get a file with the appropriate extension but the file fails to open as expected. For example, in one case I was sent some PDFs that were failing to open for a user. Adobe Reader and other PDF apps would open but the PDF file itself would not open, and no error message was presented indicating the problem. Turning to notepad, I saw the characteristic signs of the PDF signature in the top of the data. I decided to scan the bottom of the file and came across this interesting tidbit:
With that, I checked with the technical team of the website hosting the documents and found that a security API was required before the PDFs could be read. After being referred to a 3rd party website to download, the PDFs opened normally.